The invention relates to a projection exposure tool for microlithography with a measuring apparatus disposed in an optical path of the projection exposure tool. Furthermore, the invention relates to a method for measuring an irradiation strength distribution in the optical path of a projection exposure tool for microlithography.
A projection exposure tool for microlithography generally includes several optical sub-systems. These include an illumination system for illuminating a reticle carrying a structured lithography mask and a projection objective for imaging the lithography mask onto a semiconductor wafer. The illumination system has a light source, for example a laser in the UV wavelength range and a REMA objective for imaging a reticle masking device (REMA) into the reticle plane of the projection exposure tool. Therefore, the optical path of the electromagnetic radiation produced by the light source typically passes through the REMA objective, the reticle and the projection objective.
In order to measure the course of the electromagnetic radiation in the optical path of the projection exposure tool, in the prior art, cameras are positioned at points in the optical path which are accessible for this. These cameras enable locally resolved measurement of the intensity distribution of the electromagnetic radiation prevailing at the location of the camera. However, the information thus obtained regarding the course of the electromagnetic radiation is often insufficient for the optimum coordination or adjustment of the optical sub-systems.